Subject matter of this invention relates generally to limit switches and in particular to solid-state, two terminal switches utilizing infrared links.
U.S. Pat. No. 3,693,060 to Joyce issued Sept. 19, 1972 is drawn to a solid-state relay utilizing a light emitting diode to transmit visual spectrum optical energy steadily to a photosensitive solid-state element. The Joyce Patent utilizes two separate sources of power for the light emitting diode and the load. In addition, in the Joyce Patent the power supplied to the light emitting diode is not affected by the conductivity of a silicon controlled rectifier which is controllable by the light emitting diode.
U.S. Pat. No. 3,676,685 to Myer issued July 11, 1972, is drawn to a light responsive switching circuit capable of use in relatively high powered applications. The Myer Patent teaches a modularized light-responsive switching circuit capable of use in relatively high power applications. The circuit includes a Triac connected as a switching element in series with a power source and a load. The gate electrode of the Triac is connected to a light-responsive gating circuit including a capacitor and at least one light-responsive resistor switchable between two resistance levels. The capacitor is charged when the light-responsive resistor assumes one resistance level and is discharged into the gate of the Triac when the light-dependent resistor assumes the other resistance level. The components of the switching circuit are encapsulated in a cylindrical module having a screen therein, through which the active surface of the light-responsive resistor can receive light, and having a pair of terminals to connect the module directly into a power circuit.
U.S. Pat. No. 3,421,995 issued to Baker on Jan. 7, 1969, teaches an ambient light controlled solid-state relay which like the Myer Patent teaches an element in a circuit which is responsive to ambient light conditions.
U.S. Pat. No. 3,418,480 to Miller issued Dec. 24, 1968, is directed to a lighting control employing photocells and gas diodes to operate semiconductor switches. The Miller Patent is directed to a light emitting diode which is a neon bulb and a light responsive device which is a photoresistor that controls a semiconductor controlled recitifer.
All of the previous described patents teach light emitting and/or light sensitive devices used alone or in conjunction to control electrical circuitry. In the prior art electrical limit switches are taught which utilize mechanical devices in some cases and electrical devices in other cases to sense when the limits of travel or movement of a workpiece or other similar apparatus has been reached to thereby produce a force or occurrence which will cause the workpiece or similar apparatus to either stop or change direction. It is known in the prior art to provide high reliability limit switches of the type previously described by sealing them in special containers which may be oil tight or fluid tight so that limit switches may be used in environments which are exposed to oil or other substances which might foul the limit switch and cause it to foil. It would be advantageous if a limit switch were available which was highly reliable in environments of high temperature and in environments where substances such as oil may be present. Regardless of how tightly a mechanical apparatus is sealed it is possible for oil and other products to leak into the mechanism to foul it. In addition where light transmitting links are utilized in switching circuitry, the use of a relatively opaque oil base material near that circuitry may interrupt the visible light link. It would therefore also be advantageous if a highly reliable limit switch were available which is of the solid-state or static variety, which employs a means for causing a limiting function to occur which means is not adversely effected by the presence of oil nor adversely effected by the presence of heat. It would also be advantageous if this solid-state limit switch was of a two terminal variety or said in another way was adapted to be self-powered by the power in the load to be protected or switched as the case may be.